Hng dn lp trnh c bn vi Android - Bi 5
Hng dn lp trnh c bn vi Android - Bi 5
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http://diendan.vietandroid.com/cac-bai-hoc-co-kem-ma-nguon/835-huong-dan-lap-trinh-co-ban-voi-android-bai-5-a.htmlList
tutorialBi 0 - Ci t v s dng Android vi EclipseBi 1 - C bn AndroidBi
2 - Xy dng giao din n ginBi 3 - ViewGroup v Custom AdapterBi 4 -
Intent v Broadcast ReceiverBi 5 - ServiceBi 6 - SQLiteBi 7 -
Content ProviderBi 8 : Thread & Handler (Coming soon)Android
Service
4 Tutorial trc cc bn c 1 lng kin thc kha kh, tip sau y mnh xin
gii thiu 1 khi nim c bn na trong android, l Service
Service l 1 trong 4 thnh phn chnh trong 1 ng dng Android (
Activity, Service, BroadcastReceiver, ContentProvider) thnh phn ny
chy trong hu trng v lm nhng cng vic khng cn ti giao din nh chi nhc,
download, x l tnh ton
Mt Service c th c s dng theo 2 cch:
- N c th c bt u v c cho php hot ng cho n khi mt ngi no dng n li
hoc n t ngt. ch ny, n c bt u bng cch gi Context.startService() v
dng bng lnh Context.stopService(). N c th t ngt bng lnh
Service.stopSelf() hoc Service.stopSelfResult(). Ch cn mt lnh
stopService() ngng Service li cho d lnh startService() c gi ra bao
nhiu ln
- Service c th c vn hnh theo nh c lp trnh vic s dng mt Interface
m n nh ngha. Cc ngi dng thit lp mt ng truyn ti i tng Service v s
dng ng kt ni thm nhp vo Service. Kt ni ny c thit lp bng cch gi lnh
Context.bindService() v c ng li bng cch gi lnh
Context.unbindService(). Nhiu ngi dng c th kt ni ti cng mt thit b.
Nu Service vn cha c khi chy, lnh bindService() c th ty khi chy n.
Hai ch ny th khng tch bit ton b. Bn c th kt ni vi mt Service m n c
bt u vi lnh startService(). V d, mt Service nghe nhc ch nn c th c
bt u bng cch gi lnh startService() cng vi mt i tng Intent m nh dng
c m nhc chi. Ch sau , c th l khi ngi s dng mun kim sot trnh chi nhc
hoc bit thm thng tin v bi ht hin ti ang chi, th s c mt Activity to
lp mt ng truyn ti Service bng cch gi bindService(). Trong trng hp
nh th ny, stopService() s khng thc s ngng Service cho n khi lin kt
cui cng c ng li.
Ging nh mt Activity, mt Service cng c cc phng thc chu k thi gian
m bn c th ci t kim sot nhng s thay i trong trng thi ca n. Nhng nhng
phng thc ca Service th t hn l ca Activity ch c 3- v chng th c s dng
rng ri, khng c bo v.void onCreate()void onStart(Intent intent)void
onDestroy()
Bng vic thc hin nhng phng thc ny, bn c th gim st 2 vng lp ca chu
k thi gian ca mi ServiceEntire lifetime ca mt Service din ra gia
thi gian onCreate() c gi ra v thi gian m onDestroy() tr li. Ging nh
mt Activity, mt Service li tit hnh ci t ban u onCreate(), v gii
phng tt c cc ti nguyn cn li onDestroy() V d, mt Service pht li nhc
c th to ra mt lung v bt u chi nhc onCreate(),v sau lung chi nhc s
dng li onCreate(),Active lifetime ca mt Service bt u bng mt lnh ti
onStart(). yl phng thc c chuyn giao i tng Intent m c thng qua ti
startService() Service m nhc s m i tng Intent quyt nh xem s chi loi
nhc no v bt u pht nhc.Khng c callback tng ng no cho thi im Service
ngng li khng c phng thc onStop()Cc phng thc onCreate() v
onDestroy() c gi cho tt c cc Service d chng c c bt u bng
Context.startService() hoc Context.bindService() hay khng. Tuy nhin
th, onStart() ch c gi ra i vi cc Service bt u bng startService().Nu
mt Service cho php nhng Service khc kt ni vi n th s c thm cc phng
thc callback dnh cho Service thc hinIBinder onBind(Intent
intent)boolean onUnbind(Intent intent)void onRebind(Intent
intent)
Hm callback onBind() thng qua i tng Intent oc truyn n
bindService v onUnbind() c chuyn giao i tng m c chuyn n. Nu Service
ang c ch nh (binding), onBind() quay tr li knh thng tin m ngi dng s
dng tng tc vi Service. Phng thc onUnbind() c th yu cu onRebind() c
gi nu mt ngi dng kt ni vi Service
Biu di y minh ha cho cc phng thc callback ginh cho mt Service.
Mc d, n phn tch cc Service c to ra thng qua startService vi cc
Service m c to ra bng bindService(). Hy nh rng bt k Service no, cho
d n c khi to nh th no th n vn c th cho php cc ngi dng kt ni ti n mt
cch hiu qu nht, cho nn bt k Service no cng c th c ch nh thng qua cc
cc phng thc onBind()v onUnbind()
Cc bn c v hiu v Service trong Part 1. Tip theo mnh s lm 1 demo
nh cc bn hiu r hn v Service. Demo to 1 service chi nhc v ngi s dng
c th iu khin service ny.
Giao din chng trnh :
u tin l to 1 giao din iu khin service chi nhc bng layout n gin
:M:
To 1 class LocalService.java extend t Service v mt lp con
LocalBinder tha k t lp Binder ( dng iu khin service )M:public class
LocalService extends Service {
public class LocalBinder extends Binder {
LocalService getService() {
return LocalService.this;
}
}
.....
}
T np chng phng thc onBind bng cch tr li gi tr mBinderM: private
final IBinder mBinder = new LocalBinder();
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
To mt i tng MediaPlayer chi nhc n gin ( s dng chi file abc.mp3 t
trong folderres/raw):M:MediaPlayer mMediaPlayer;
public void startMp3Player() {
mMediaPlayer = MediaPlayer.create(getApplicationContext(),
R.raw.abc);
mMediaPlayer.start();
}
public void mp3Stop() {
mMediaPlayer.stop();
mMediaPlayer.release();
}
lp LocalServiceBinding.java extend t lp Activity chng ta ch cn n
i tng mConnection c nhim v gim st kt ni ca service chi nhc.M:
private ServiceConnection mConnection = new ServiceConnection()
{
public void onServiceConnected(ComponentName className, IBinder
service) {
mBoundService =
((LocalService.LocalBinder)service).getService();
Toast.makeText(LocalServiceBinding.this,
R.string.local_service_connected,
Toast.LENGTH_SHORT).show();
}
public void onServiceDisconnected(ComponentName className) {
mBoundService = null;
Toast.makeText(LocalServiceBinding.this,
R.string.local_service_disconnected,
Toast.LENGTH_SHORT).show();
}
};
V x l s kin 3 button ( Bind, Unbin, Play/Stop )M: private
OnClickListener mBindListener = new OnClickListener() {
public void onClick(View v) {
bindService(new Intent(LocalServiceBinding.this,
LocalService.class), mConnection, Context.BIND_AUTO_CREATE);
mIsBound = true;
mPlayButton.setEnabled(true);
}
};
private OnClickListener mPlayListener = new OnClickListener()
{
public void onClick(View v) {
if(mPlayButton.getText() == "Play")
{
mBoundService.startMp3Player();
mPlayButton.setText("Stop");
}
else
{
mBoundService.mp3Stop();
mPlayButton.setText("Play");
}
}
};
private OnClickListener mUnbindListener = new OnClickListener()
{
public void onClick(View v) {
if (mIsBound) {
unbindService(mConnection);
mIsBound = false;
mPlayButton.setEnabled(false);
}
}
};
SourceCode :http://www.mediafire.com/?ymyyiynizlzP/S: Nh eo
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